Context & Key Findings
- A study published in Nature Reviews Biodiversity shows rapid spread of alien plant species, especially in tropical regions.
- These alien species are outcompeting and replacing native flora, leading to irreversible ecosystem changes.
- Human activities and climate change are key drivers accelerating the invasion.
What are Alien Plant Species?
- Non-native plants introduced intentionally or accidentally by humans into new regions.
- Often lack natural predators in the new ecosystem, allowing unchecked proliferation.
- Examples: Prosopis juliflora, Lantana camara, Chromolaena odorata, Ziziphus mauritiana, Vachellia nilotica.
Impact on Tropical Ecosystems
- Focus is on the Greater Tropics (tropics + subtropics) — 60% of Earth’s land area and home to the majority of biodiversity.
- Over 9,831 alien plant species are now established in the Greater Tropics.
- 26% of islands globally now have more alien than native flora. E.g., Tahiti (73.8%), Guam (66.5%), Hawaii, Madagascar.
Environmental Impacts
- Alien plants are altering fire regimes (increasing fire frequency/intensity).
- Increase in atmospheric CO₂ → higher plant biomass → more invasive woody growth.
- Example: Brachiaria decumbens in Amazon fuels intense fires → forest degradation → feedback loop for more invasions.
Impacts in India
- Around 66% of India’s natural systems (~750,000 km²) already affected by alien plant invasions.
- Land use change (agriculture, settlements) has modified fire and herbivory regimes, making conditions ripe for invasions.
- Example: Prosopis juliflora provides food for blackbuck, which unknowingly disperses alien seeds, harming native plants.
- Forest thickening by alien plants leads to higher wildfire risk in savannas and open forests.
Global Trends & Projections
- Since 1950s: exponential rise in invasions; 13,939–18,543 alien species already outside native ranges.
- By 2050, new invasions expected to rise:
- 21% in South America
- 12% in Africa
- 10% in tropical Asia
- Predicts growing ecosystem homogenization, leading to biodiversity loss.
Drivers of Invasion
- Climate change: Hotter days, extreme heat, droughts, forest diebacks.
- Anthropogenic factors: Agriculture, urban expansion, historical plantations, poor regulation of plant imports.
- Weakening biotic resistance and rising CO₂ levels are creating ideal conditions for invasions.
Policy & Economic Challenges
- Alien species control in India would require US $13.5 billion — 36× its current environmental budget.
- Current responses are fragmented and lack long-term planning.
Way Forward: Recommendations
- Urgent interdisciplinary studies across the Greater Tropics.
- Strengthened regulation, monitoring, and early detection.
- Ecosystem restoration and community awareness, especially in the Global South.
- Emphasis on understanding native invaders and interactions with local fauna.
